This invention pertains to flexible floating covers for covering large liquid reservoirs, and particularly it relates to a floating cover which is anchored to the perimeter walls of a reservoir and which rises and falls with the liquid level inside the reservoir.
Floating covers are mounted over settling ponds and clarifiers to contain and collect fermentation gases of mill effluent for example. Floating covers are also mounted over water reservoirs to prevent contamination of potable water from acid rain, pollen, leaves, dust, insects, bird droppings, the effect of sunlight and from the activities of other animals.
The installation of a floating cover over a large liquid reservoir represents certain difficulties in that the cover is exposed to the elements and to the movement of the liquid under the cover. For example, a slight accumulation of rain over a cover creates puddles and mounds which catch the wind and promote waves along the cover and into the liquid under the cover. The movement of liquid under the cover causes tangential stresses and constant movement in the cover. These stresses could cause fatigue, localized elongation and rupture of the cover. The formation of mounds and puddles on a floating cover is amplified where the cover is installed over a reservoir that could have gases coming out of the liquid inside the reservoir.
Examples of floating covers of the prior art are described in the following documents:
U.S. Pat. No. 3,313,443, issued on Apr. 11, 1967 to H. S. Dial et al.;
U.S. Pat. No. 3,683,428, issued on Aug. 15, 1972 to L. Morris;
U.S. Pat. No. 3,980,199, issued on Sep. 14, 1976 to W. B. Kays;
U.S. Pat. No. 4,139,117, issued on Feb. 13, 1979 to H. S. Dial;
U.S. Pat. No. 4,181,986, issued on Jan. 8, 1980 to H. E. Aine;
U.S. Pat. No. 4,192,025, issued on Mar. 11, 1980 to C. A. Hinsperger;
U.S. Pat. No. 4,438,863, issued on Mar. 27, 1984 to J. V. Wilson et al.;
U.S. Pat. No. 4,503,988, issued on Mar. 12, 1985 to D. H. Gerber;
U.S. Pat. No. 4,603,790, issued on Aug. 5, 1986 to D. H. Gerber;
U.S. Pat. No. 4,672,691, issued on Jun. 16, 1987 to De Garie et al.;
U.S. Pat. No. 5,505,848, issued on Apr. 9, 1996 to Landine et al.;
U.S. Pat. No. 5,587,080, issued on Dec. 24, 1996 to Landine et al.
A common method in the prior art for supporting a floating cover over a reservoir consists of bonding float blocks to the underside of the impermeable membrane, or positioning float blocks inside pockets formed in the membrane. This method has had limited success in the past because the float blocks and pockets cause obstructions which catch the liquid movement under the cover and apply tearing stresses along the surface of the cover. Where the cover is installed over a clarifier or a pond and scum tends to form at the surface of the pond, the wind-induced movement in the liquid of the pond and associated scum movement under the cover generate forces that can rip a float block or a pocket away, and tear the strongest impermeable membrane.
Therefore, it is believed that there is a need in the industry for a better flexible floating cover which is adapted to minimize the formation of puddles and mounts thereon and which is less susceptible of generating destructive stresses from wind-induced liquid movement under the cover.
In the present invention, there is provided a floating cover for liquid reservoir wherein the structure of the cover is particularly flexible to follow the movement of the liquid inside the reservoir without generating excessive tangential stress in the water-impermeable membrane of the cover. Specific segments of the cover become quickly submersed during a rainstorm to keep the cover membrane taut and to limit the formation of randomly spaced puddles that can deform the cover and create stresses in the cover membrane.
In a first aspect of the present invention there is provided a liquid reservoir having a floating cover mounted thereon. The floating cover has a floating grid anchored to the perimeter walls of the reservoir. The floating grid floats over the liquid inside the reservoir. The floating grid comprises a keel member and an array of buoyant beams affixed to the keel member and extending away from the keel member. A water-impermeable membrane is affixed to the perimeter wall and is loosely laid over the floating grid. There is also provided an array of weight lines anchored to the perimeter walls and loosely laid over the impermeable membrane. Each of the weight lines is laid at about halfway between an adjacent pair of the buoyant beams.
The primary advantage of this structure is that the floating grid, the impermeable membrane and the array of weight lines constitute three separate layers that are loosely laid over each other. These three separate layers are therefore free to slide upon each other and flex to follow the movement of the liquid inside the reservoir without generating any destructive tangential stress in the impermeable membrane.
In another feature of the present invention, the buoyant beams and the weight lines are flexible longitudinally whereby a relative movement of the impermeable membrane between the floating grid and the array of weight lines does not generate any point of concentrated shear stresses in the impermeable membrane.
In still another feature of the present invention, the impermeable membrane has segments that are quickly submersed under the liquid level during a rainstorm. The submersed segments extend along the keel member and along the weight lines. These submersed segments are advantageous for keeping the impermeable membrane in a taut condition during a rainstorm, and for reducing the formation of puddles and mounds thereon.
In accordance with yet another feature of the present invention, the impermeable membrane has a series of drain holes therein. The drain holes are located in a central one third portion of the width of the impermeable membrane. Due to the location of these drain holes, the submersed segments remain present on the impermeable membrane for extended period of time following a rainstorm. Furthermore, the drain holes in the cover of the present invention represent a distinct advantage over the traditional use of hazardous electrical sump pumps.
Other advantages and novel features of the present invention will become apparent from the following detailed description.